Right, so when I did my sound system a few years ago, I was a little careless and while I was enlarging the tweeter hole to fit my new tweeters, I took off a little too much plastic on certain areas. I could buy new sail panels but that would be $33x2. Not too bad but still, does anyone know of a place I could get small black plastic flat rings where the inside diameter is 1" (tweeter size) and the ring part is say... 3mm? That way I could put the ring down before inserting the tweeter, and the ring would cover up the lovely botched job I did...

Not sure what a ring like that would be called... anybody know?

(I googled black plastic o-ring 1" opening, found a bunch of stuff but it's all "nickel plastic" and shiny...)

 

https://www.google.com/search?q=1"+rubber+grommet

check out google images

 

You don't need to do that. Just use a two part 'rigid plastic repair' kit (3M), and treat it like bodywork. I molded my Massive CK6 tweeters right into the sail panels, and retained the 'eyeball' adjustability of the tweeter housing (the tweeter can be moved both up and down and left/right to fine tune the sound stage). Once I moulded the tweeter housing into the sail panel, I sprayed it with textured black paint for plastic...turned out perfect:

 

I did the same thing in my last car (a VW Passat): cut rough hole, stuck the tweeter mounting cup in, fill in all the ugly gaps with plain old Bondo, sanded for days, then sanded some more primed, sanded again and painted with truck bedliner black textured paint. Then just snapped each tweeter in, rotated as desired and it looked totally OEM. These were smallish Polk tweeters and would have looked fine just mounted normally, but I wanted a super clean factory look thus blending the mounts into the factory plastic was key to pulling that off.

In my Z however I went totally stealth and found a tweeter (JL Audio C2s) that fit behind the pillar (in the original factory location) perfectly.